IP telephony allows people to use the Internet as the transmission medium for telephone calls. The basic steps involved in originating an IP telephone call are conversion of the analog voice signal to digital format, and compression/translation of the signal into IP data packets for transmission over the Internet, with the process being reversed at the receiving end. Each IP data packet may be transmitted between two endpoints directly or via one or more IP telephony gateways. Accordingly, an IP telephony gateway may host multiple IP telephone calls.
Network monitors and network sniffing tools are designed to capture IP packets from the network. For example, these tools may be used to capture packets between two H.323 entities. An H.323 entity is an entity that follows an H.323 protocol, which is defined by Telecom Standard H.323 of the International Telecommunication Union (ITU-T). H.323 describes terminals, equipment and services for multimedia communication over networks. Computer terminals and equipment that fulfill H.323 may carry real-time voice, data and video, or any combination including, for example, video telephony.
Some network monitors and network sniffing tools may include parsers for filtering IP data packets such as H.323 Protocol Data Units (PDUs) and may be used to assist software engineers in debugging IP telephony applications. This assistance, however, has proven to be insufficient in a multiple-call environment.